Sustained release microcapsule

ABSTRACT

Microcapsules are advantageously produced with high take-up of a water-soluble drug by preparing a W/O emulsion composed of a water-soluble drug-containing solution as the inner aqueous phase and a polymer-containing solution as the oil phase, dispersing said emulsion in an aqueous phase and subjecting the resulting W/O/W emulsion to an in-water drying, wherein the viscosity of the W/O emulsion used in preparing the W/O/W emulsion is adjusted to about 150 to about 10,000 centipoises.

This application is a continuation of U.S. application Ser. No.07/541,067 filed Jun. 20, 1990, now abandoned, which is a divisional ofSer. No. 07/249,198, filed Sep. 23, 1988, U.S. Pat. No. 4,954,298, whichis a continuation of Ser. No. 06/826,968, filed Feb. 7, 1986, abandoned.

This invention relates to a method for producing sustained-releasemicrocapsules containing a water-soluble drug.

For drugs required to be administered for a prolonged period, variousdosage forms have been proposed. Among them, there is disclosed inEuropean Patent Application Publication No. 52,510A a method ofmicroencapsulation by phase separation using a coacervation agent suchas a mineral oil or a vegetable oil.

Microcapsules obtained by the above-mentioned method have a drawback inthat the particles are apt to adhere to one another in their productionprocess.

Under these circumstances, the intensive studies were curried out inorder to develop sustained release drug preparations. As a result, itwas found that microcapsules having favorable properties can be obtainedefficiently with a high rate of drug take-up into the microcapsuleswhen, in the process of forming a three-phase emulsion formicroencapsulation by an in-water drying, the viscosity of the W/Oemulsion for preparing the three-phase W/O/W emulsion is adjusted toabout 150 to about 10,000 cp. Further research work based on thisfinding has now led to completion of the present invention.

Thus this invention is directed to: a method of preparingsustained-release microcapsules containing a water-soluble drug, whichcomprises preparing a W/O emulsion composed of a water-solubledrug-containing solution as the inner aqueous phase and apolymer-containing solution as the oil phase adjusting the viscosity ofthe W/O emulsion used in preparing the W/O/W emulsion to from about 150to about 10,000 cp, dispersing said emulsion in an aqueous phase andsubjecting the resulting W/O/W emulsion to an in-water drying.

The viscosity value mentioned herein is measured with an Ubbelohdeviscometer in accordance with the Japanese Pharmacopeia. This is dynamicviscosity value, and "cp" stands for centipoise.

The water-soluble drug to be used in the practice of this invention ishighly hydrophilic and has a small oil/water distribution coefficientwhich, when given in terms of octanol/water distribution coefficient,for instance, is not greater than about 0.1.

Said water-soluble drug includes, but is not particularly limited to,physiologically active polypeptides, other antibiotics, antitumoragents, antipyretics, analgesics, antiinflammatory agents, antitussivesand expectorants, sedatives, muscle relaxants, antiepileptics, antiulceragents, antidepressants, antiallergic agents, cardiotonics,antiarrhythmic agents, vasodilators, antihypotensive diuretics,antidiabetic agents, anticoagulants, hemostatic agents, antitubercularagents, hormones and narcotic antagonists.

The physiologically active polypeptides usable in the practice of thisinvention contain two or more amino acids and preferably have amolecular weight of about 200 to about 80,000.

Examples of said polypeptides include luteinizing hormone releasinghormone (LH-RH), derivatives thereof having LH-RH like activity, i.e.the polypeptides of the formula:

    (Pyr)Glu--R.sub.1 --Trp--Ser--R.sub.2 --R.sub.3 --R.sub.4 --Arg--Pro--R.sub.5                                       (I)

wherein R₁ is His, Tyr, Trp or p-NH₂ -Phe, R₂ is Tyr or Phe, R₃ is Glyor a D-amino acid residue, R₄ is Leu, Ile or Nle and R₅ is Gly-NH-R₆ (R₆is H or a lower alkyl group which may optionally be substituted byhydroxy) or NH-R₆ (R₆ is as defined above), and salts thereof [see U.S.Pat. Nos. 3,853,837, 4,008,209 and 3,972,859, British Patent No.1,423,083, and Proceedings of the National Academy of Sciences of theUnited States of America, volume 78, pages 6509-6512 (1981)].

Referring to the above formula (I), the D-amino acid residue representedby R₃ is, for example, an α-D-amino acid residue containing up to 9carbon atoms (e.g. D-Leu, Ile, Nle, Val, NVal, Abu, Phe, Phg, Ser, Tyr,Met, Ala, Trp, α-Aibu). It may have an appropriate protective group(e.g. t-butyl, t-butoxy, t-butoxycarbonyl, naphtyl). An acid additionsalt or metal complex of the peptide (I) can of course be used in thesame manner as the peptide (I).

In abbreviating the amino acids, peptides, protective groups and so onas used in specifying the polypeptides of formula (I), there are usedthe abbreviations according to the IUPAC-IUB Commission on BiologicalNomenclature or the abbreviations commonly used in the relevant field ofart. For those amino acids which involve optical isomerism, eachabbreviation, unless otherwise indicated, refers to the L-form.

In this specification, the acetate of the polypeptide of the aboveformula (I) wherein R₁ =His, R₂ =Tyr, R₃ =D-Leu, R₄ =Leu and R₅ = NHCH₂--CH₃ is called "TAP-144". Said polypeptide in acetate form has thegeneric name "leuprolide".

Said polypeptides further include LH-RH antagonists (see U.S. Pat. Nos.4,086,219, 4,124,577, 4,253,997, 4,317,815, 329,526 and 368,702).

Said polypeptides also include, for example, insulin, somatostatin,somatostatin derivatives (see U.S. Pat. Nos. 4,087,390, 4,093,574,4,100,117 and 4,253,998), growth hormones, prolactin,adrenocorticotropic hormone (ACTH), melanocyte-stimulating hormone(MSH), thyrotropin-releasing hormone (TRH), salts and derivativesthereof (see U.S. Pat. Nos. 3,957,247 and 4,100,152),thyroid-stimulating hormone (TSH), luteinizing hormone (LH),follicle-stimulating hormone (FSH), vasopressin, vasopressin derivatives[desmopressin [see Folia Endocrinologica Japonica, volume 54, No. 5,pages 676-691 (1978)]], oxytocin, calcitonin, parathyroid hormone,glucagon, gastrin, secretin, pancreozymin, cholecystokinin, angiotensin,human placental lactogen, human chorionic gonadotropin (HCG),enkephalin, enkephalin derivatives (see U.S. Pat. No. 4,277,394 andEuropean Patent Application Publication No. 31567A), endorphin,kyotorphin, interferons (α, β and γ), interleukins (I, II and III),taftsin, thymopoietin, thymosin, thymostimulin, thymic humoral factor(THF), serum thymic factor (STF or FTS) and derivatives thereof (seeU.S. Pat. No. 4,229,438), and other thymic factors [Igaku no Ayumi(Medicine in Progress), volume 125, No. 10, pages 835-843 (1983)], tumornecrosis factor (TNF), colony stimulating factor (CSF), motilin,dinorphin, bombesin, neurotensin, cerulein, bradykinin, urokinase,asparaginase, kallikrein, substance P, nerve growth factor, bloodcoagulation factors VIII and IX, lysozyme chloride, polymixin B,colistin, gramicidin, bacitracin, protein synthesis-stimulating peptides(British Patent No. 8,232,082), gastric inhibitory polypeptide (GIP),vasoactive intestinal polypeptide (VIP), platelet-derived growth factor(PDGF), growth hormone-releasing factor (GRF, somatocrinin), bonemorphagenetic protein (BMP) and epidermal growth factor (EGF).

The antitumor agents mentioned above include, among others, bleomycinhydrochloride, methotrexate, actinomycin D, mitomycin C, vinblastinesulfate, vincristine sulfate, daunorubicin hydrochloride, adriamycin,neocarcinostatin, cytosine arabinoside, fluorouracil,tetrahydrofuryl-5-fluorouracil, krestin, picibanil lentinan, levamisole,bestatin, azimexon, glycyrrhizin, poly I:C, poly A:U and poly ICLC.

The antibiotics mentioned above include, among others, gentamicin,dibekacin, kanendomycin, lividomycin, tobramycin, amikacin, fradiomycin,sisomicin, tetracycline hydrochloride, oxytetracycline hydrochloride,rolitetracycline, doxycycine hydrochloride, ampicillin, piperacillin,ticarcillin, cephalotin, cephaloridine, cefotiarn, cefsulodine,cefmenoxime, cefmetazole, cefazolin, cefotaxime, cefoperazone,ceftizoxime, moxalactam, thienamycin, sulfazecin and azthreonam.

The antipyretic, analgesic and antiinflammatory agents mentioned aboveinclude, among others, sodium salicylate, sulpyrine, sodium flufenamate,sodium diclofenac, sodium indomethacin, morphine hydrochloride,pethidine hydrochloride, levorphanol tartrate and oxymorphone. Theantitussives and expectorants include ephedrine hydrochloride,methylephedrine hydrochloride, noscapine hydrochloride, codeinephosphate, dihydrocodeine phosphate, alloclamide hydrochloride,chlophedianol hydrochloride, picoperidamine hydrochloride, cloperastine,protokylol hydrochloride, isoproterenol hydrochloride, salbutamolsulfate and terbutaline sulfate, among others. The sedatives includechlorpromazine hydrochloride, prochlorperazine, trifluoperazine,atropine sulfate, scopolamine methyl bromide, and so forth. The musclerelaxants include, for example, pridinol methanesulfonate, tubocurarinechloride and pancuronium bromide. The antiepileptics include sodiumphenytoin, ethosuximide, sodium acetazolamide chlordiazepoxidehydrochloride, etc. The antiulcer agents include, among others,metoclopramide and histidine hydrochloride. The antidepressants includeimipramine, clomipramine, noxiptiline and phenelzine sulfate, amongstothers. The antiallergic agents include, for instance, diphenhydraminehydrochloride, chlorpheniramine maleate, tripelenamine hydrochloride,methdilazine hydrochloride, clemizole hydrochloride, diphenylpyralinehydrochloride and methoxyphenamine hydrochloride. The cardiotonicsinclude, among others, trans-π-oxocamphor, theophillol, amihophyllineand etilefrine hydrochloride. The antiarrhythmic agents includepropranolol hydrochloride, alprenolol hydrochloride, bufetololhydrochloride, oxyprenolol hydrochloride, etc. The vasodilators includeoxyfedrine hydrochloride, diltiazem hydrochloride, tolazolinehydrochloride, hexobendine and bamethan sulfate, among others. Thehypotensive diuretics include hexamethonium bromide, pentolinium,mecamylamine hydrochloride, ecarazine hydrochloride, clonidinehydrochloride, etc. The antidiuretic agents include, among others,sodium glymidine, glypizide, phenformin hydrochloride, buforminhydrochloride and metformin. The anticoagulants include sodium heparinand sodium citrate, among others. The hemostatic agents includethromboplastin, thrombin, menadione sodium bisulfite, acetomenaphthone,ε-aminocaproic acid, tranexamic acid, carbozochrome sodium sulfate,adrenochrome monoaminoguanidine methanesulfonate, and so forth. Theantituberculous agents include, among others, isoniazide, ethanbutol andsodium p-aminosalicylate. The hormones include, among others,prednisolone succinate, prednisolone sodium phosphate, dexamethasonesodium sulfate, betamethasone sodium phosphate, hexestrol diphosphate,hexestrol diacetate and methimazole. The narcotic antagonists includelevallorphan tartrate, nalorphine hydrochloride and neloxonehydrochloride, among others.

The above-mentioned water-soluble drugs are used in amounts selecteddepending on the kind of drug, desired pharmacological effects andduration of the effects, among others, and the concentration in theinner aqueous phase is selected generally within the range about 0.001%to about 70% (weight/weight), preferably within the range of 0.01%. to50% (weight/weight).

In carrying out the method according to this invention, the viscosity ofthe inner aqueous phase may be increased by further adding a drugretaining substance to the inner aqueous phase.

The drug retaining substance mentioned above is a substance which issoluble in water but is hardly soluble in the organic solvent in the oilphase and, when dissolved in water, gives a highly viscous semisolid or,when placed in a water-dissolved state under the action of some externalfactor, for instance temperature, pH, metal ion (e.g. Cu⁺⁺, Al⁺⁺⁺,Zn⁺⁺), organic acid (e.g. tartaric acid, citric acid, tannic acid) orsalt thereof (e.g. calcium citrate) or chemical condensing agent (e.g.glutaraldehyde, acetaldehyde), gives a semisolid or solid matrix as aresult of marked increase of viscosity caused by said external factor.

Examples of said drug retaining substance are natural or synthetic gumsor high-molecular compounds.

The natural gums include gum acacia, Irish moss, karaya gum, gumtragacanth, gum guaiac, xanthan gum and locust bean gum. The naturalhigh molecular compounds include proteins, such as casein, gelatin,collagen, albumin (e.g. human serum albumin), globulin and fibrin, andcarbohydrates, such as cellulose, dextrin, pectin, starch, agar andmannan. They may be used either as such or in the form of synthetic gumsresulting from partial chemical modification, for example esters orethers derived from the above-mentioned natural gums (e.g.methylcellulose, ethylcellulose, carboxymethylcellulose, gelatinsuccinate), hydrolyzates thereof (e.g. sodium alginate, sodiumpectinate), or salts of these.

The synthetic high-molecular compounds include, among others, polyvinylcompounds (e.g. polyvinyl pyrrolidone, polyvinyl alcohol, polyvinylmethyl ether, polyvinyl ether), polycarboxylic acids [e.g. polyacrylicacid, polymethacrylic acid, Carbopol (Goodrich)], polyethylene compounds(e.g. polyethylene glycol), polysaccharides (e.g. polysucrose,polyglucose, polylactose), and salts of these.

Also included within the scope of drug retaining substances aresubstances capable of giving high-molecular compounds as a result ofcondensation or cross-linking which proceeds under the action of theexternal factor mentioned above.

Among these drug retaining substances, there are particularly preferablegelatin, albumin, pectin and agar. The drug retaining substances may beused either alone or in combination.

The polymer to be contained in the oil phase in carrying out the methodaccording to this invention is a polymer which is scarcely soluble orinsoluble in water and is biocompatible. Examples are such biodegradablepolymers as aliphatic polymers (e.g. polylactic acid, polyglycolic acid,polycitric acid, polymalic acid), poly-α-cyanoacrylic acid esters,poly-β-hydroxybutyric acid, polyalkylene oxalate (e.g. polytrimethyleneoxalate, polytetramethylene oxalate), polyorthoesters,polyorthocarbonates and other polycarbonates (e.g. polyethylenecarbonate, polyethylene-propylene carbonate), and polyamino acids (e.g.poly-γ-benzyl-L-glutamic acid, poly-L-alanine, poly-γ-methyl-L-glutamicacid). Other biocompatible high polymers are polystyrene, polyacrylicacid, polymethacrylic acid, acrylic acid-methacrylic acid copolymers,polyamides (nylon), polyethylene terephthalate (tetron), polyaminoacids, silicone polymers, dextran stearate, ethylcellulose,acetylcellulose, nitrocellulose, polyurethanes, maleic anhydride-basedcopolymers, ethylenesvinyl acetate copolymers, polyvinyl acetate,polyvinyl alcohol, polyacrylamide, etc. These polymers may behomopolymers or copolymers of two or more monomers, or mixtures of thepolymers. They may also be in the salt form.

Among these polymers, particularly preferred for use in injections arebiodegradable polymers, most preferably polylactic acid, lacticacid-glycolic acid copolymer and mixtures thereof.

The ratio of lactic acid to glycolic acid in the copolymer is preferablyabout 100/0 to 50/50 (weight %) preferably about 50 to 95 weight % oflactic acid and about 50 to 5 weight % of glycolic acid, more preferablyabout 60 to 95 weight % of lactic acid and about 40 to 5 weight % ofglycolic acid, still more preferably about 60 to 85 weight % of lacticacid and about 40 to 15 weight % of glycolic acid. The ratio isespecially preferably about 75±2 mole % of lactic acid and about 25±2mole % of glycolic acid.

The polymers for use in this invention preferably have an averagemolecular weight of about 1,000 to about 800,000, more preferably about2,000 to about 100,000.

The lactic acid-glycolic acid copolymers still more preferably have anaverage molecular weight of about 5000 to about 30000.

These polymers are used in amounts to be selected depending on theintensity of pharmacological activity of the water-soluble drug, drugrelease rate, the duration and other factors. For instance, these areused as the microcapsule bases in an amount of about 3 to 10,000 partsby weight, preferably about 5 to about 100 parts by weight, per partby-weight of the water-soluble drug.

The solution (oil phase) containing the above polymer is that of thepolymer in an organic solvent.

Said organic solvent may be any organic sovlent which has a boilingpoint not higher than about 120° C. and hardly miscible with water.Examples are halogenated alkanes (e.g. dichloromethane, chloroform,chloroethane, trichloroethane, carbon tetrachloride), ethyl acetate,ethyl ether, cyclohexane, benzene, and toluene. These may be used inadmixture of two or more.

In carrying out the microencapsulation method according to thisinvention, water is added to the water-soluble drug to prepare the inneraqueous phase. Here, the above-mentioned drug retaining substance mayfurther be added. To said inner aqueous phase, there may be added apH-adjusting agent for maintaining the stability or solubility of thewater-soluble drug, such as carbonic acid, acetic acid, oxalic acid,citric acid, tartaric acid, succinic acid, phosphoric acid, the sodiumor potassium salt of the above compound, hydrochloric acid or sodiumhydroxide. There may further be added a stabilizer for the water-solubledrug such as albumin, gelatin, citric acid, sodiumethylenediaminetetraacetate, dextrin or sodium hydrogen sulfite, or apreservative such as a para-hydroxybenzoic acid ester (e.g.methylparaben, propylparaben), benzyl alcohol, chlorobutanol orthimerosal.

The thus-obtained aqueous solution for use as the inner aqueous phase isadded to a polymer-containing solution (oil phase), followed by anemulsification procedure to give a W/O emulsion.

For said emulsification procedure, a known method of effectingdispersion is used. Said method is, for example, the intermittentshaking method, the mixer method using a propeller-shaped stirrer, aturbine-shaped stirrer or the like, the colloid mill method, thehomogenizer method or the ultrasonication method.

The thus-prepared W/O emulsion is them emulsified into a W/O/Wtriplicate-phase emulsion and subjected to an in-water drying. Thus,said W/O emulsion is further added to a third aqueous phase to give aW/O/W emulsion and thereafter the solvent in the oil phase is removed togive microcapsules.

To the external aqueous phase, there may be added an emulsifying agent.As the emulsifying agent, there may be used any one capable of forminggenerally a stable O/W emulsion, for example-an anionic surfactant (e.g.sodium oleate, sodium stearate, sodium lauryl sulfate), a nonionicsurfactant [e.g. polyoxyethylenesorbitan fatty acid ester (Tween 80,Tween 60, products of Atlas Powder Co., U.S.A.), a polyoxyethylenecastor oil derivative (HCO-60, HCO-50, products of Nikko Chemicals,Japan)], polyvinyl pyrrolidone, polyvinyl alcohol,carboxymethylcellulose, lecithin or gelatin. Such emulsifiers may beused either alone or in combination of some of them. The emulsifyingagent concentration may suitably be selected within the range of about0.01% to 20%, preferably within the range of about 0.05% to 10%.

The viscosity of the W/O emulsion for preparing the W/O/W emulsion isadjusted to about 150 cp to 10,000 cp, preferably about 150 cp to 5,000cp. In adjusting the viscosity, there may be used the following means ora combination thereof for instance:

To increase the polymer concentration in the oil phase;

To adjust the ratio in amount between the aqueous phase and the oilphase;

To adjust the temperature of said W/O emulsion;

To adjust the temperature of the-external aqueous phase; or

To adjust the temperature of the W/O emulsion with a line heater orcooler or the like in infusing the W/O emulsion into the externalaqueous phase.

What is important in taking such measures as mentioned above is onlythat the W/O emulsion has a viscosity of about 150 cp to 10,000 cp whenit is made up into a W/O/W emulsion.

In adjusting the viscosity of the W/O emulsion by taking one or more ofthe above procedures, the polymer concentration in the oil phase, whenadjusted, is preferably adjusted to about 10 to 80% (weight by weight),although the preferable range of such concentration is not specifiedgenerally but may vary depending on the kind of polymer, kind of solventand other factors.

The adjusting the viscosity of the W/O emulsion in the above manner ispreferably carried out so that the W/O ratio falls within the range ofabout 1% to 50% (volume by volume), although the preferable range ofsuch ratio is not specified generally but may depend on the kind andamount of water-soluble drug and properties of the oil phase.

In adjusting the viscosity of the W/O emulsion in the above manner, thetemperature of the W/O emulsion is generally regulated to from about-20° C. to the boiling point of the organic solvent used, preferablyabout 0° C. to 30° C.

In cases where the polymer concentration in the oil phase has beenadjusted or in cases where the ratio between the aqueous phase and theoil phase has been adjusted, the viscosity of the W/O emulsion can bealso adjusted on the occasion of preparing the W/O emulsion.

In cases where the viscosity of the W/O emulsion is adjusted byregulating the temperature of the W/O emulsion, the temperature of saidW/O emulsion is adjusted, for example on the Occasion of adding the W/Oemulsion to the external aqueous phase. The viscosity adjustment mayalso be effected by adjusting in advance the temperature of the externalaqueous phase on the occasion of adding the W/O emulsion to the externalaqueous phase so that the temperature of the W/O emulsion can beadjusted when the W/O/W emulsion is prepared.

For removing the solvent from the oil phase in subjecting the W/O/Wemulsion to an in-water drying, any of the common methods in general useis employed. Thus, the solvent is removed, for example by simplyallowing the W/O/W emulsion to stand under stirring, by heating slowlysaid emulsion, by blowing nitrogen gas or the like onto said emulsion,by gradually reducing the pressure while stirring with apropeller-shaped stirrer or a magnetic stirrer, or by using a rotaryevaporator while adjusting the degree of vacuum. In the step of solventremoval, the required time can be reduced by gradually warming the W/O/Wemulsion after the progress of solidification of the polymer to acertain extent, to thereby rendering the solvent removal more complete.

The thus-produced microcapsules are collected by centrifugation orfiltration, rinsed several times with distilled water to thereby removethe free water-soluble drug portion adhering to the microcapsule surfaceand other substances, and, if necessary, warmed under reduced pressureto thereby remove the moisture in microcapsules and the solvent in themicrocapsule wall more completely.

The microcapsules obtained in the above manner are sieved as necessaryto eliminate excessively large microcapsules. For use in the form ofsuspensions depending on the extent of the sustained-release property,the microcapsules may have a grain size within the range in which thedispersibility and penetration requirements are met. Thus, for example,they may have an average grain size within the range of about 0.5 to 400μm, desirably and preferably within the range of about 2 to 200 μm, morepreferably about 2 to 100 μm.

In this manner, the rate of take-up of the water-soluble drug, which isthe active ingredient, into microcapsules can be increased by using themethod according to this invention. Furthermore, the use of a smalleramount of organic solvent in the production process is sufficient ascompared with the process involving drying in the oil phase. From theabove and other viewpoints, the method according to this invention isadvantageous in commercial microcapsule production.

The microcapsules produced by the method according to this inventionhave many advantages. For instance, they scarcely undergo aggregation orcohesion to one another during the production step. There can beobtained microcapsules which are satisfactorily spherical in shape. Thestep of removing the solvent from the oil phase is easy to control,whereby the surface structure of microcapsules , which is decisive forthe rate of drug release (inclusive, e.g. of the number and size ofpores which are to serve as main routes of drug release), can becontrolled.

The microcapsules produced by the method according to this invention canbe administered to the living body by implantation thereof as such. Theymay also be administered in various dosage forms and thus can be used asraw material in producing such dosage forms.

The injection form is preferably as the dosage form mentioned above.

For instance, in making up the microcapsules according to this inventionfor an injection, the microcapsules according to the invention aredispersed in an aqueous medium together with a dispersing agent (e.g.Tween 80, HCO-60, carboxymethylcellulose, sodium alginate), apreservative (e.g. methylparaben, propylparaben), an isotonizing agent(e.g. sodium chloride, mannitol, sorbitol, glucose). Such suspension canserve as a sustained-release injection.

Furthermore, the above microencapsulated sustained-release injection canbe converted to a more stable, sustained-release injection by adding anadditional excipient (e.g. mannitol, sorbitol, lactose, glucose),redispersing the resulting mixture and effecting solidification byfreeze drying or spray drying with simultaneous addition of distilledwater for injection or some appropriate dispersing agent.

The dose of the sustained-release preparation according to thisinvention may vary depending on the kind and amount of the water-solubledrug, which is the active-ingredient, dosage form, duration of drugrelease, recipient animal (e.g. warm-blooded animals such as mouse, rat,horse, cattle, human) and purpose of administration but should be withinthe range of effective dose of said active ingredient. For example, thesingle dose per said animal of the microcapsules can adequately beselected within the range of about 0.01 to 200 mg/kg body weight,preferably about 0.2 to 40 mg/kg, still more preferably about 0.2 to 20mg/kg or 0.2 to 6 mg/kg. The volume of the suspension for administeringas the above-mentioned injection can adequately be selected within therange of about 0.1 to 10 ml, preferably about 0.1 to 5 ml, morepreferably about 0.5 to3 ml.

In this manner, there is obtained a pharmaceutical composition preparedin the form of microcapsules which comprises an effective but greateramount of the water-soluble drug as compared with the ordinary singledose and a biocompatible high polymer and is capable of releasing thedrug continuously over a prolonged period of time.

The sustained-release preparation according to the present invention hasthe following advantages, among others:

(1) Sustained-release of the water-soluble drug can be attained invarious dosage forms. In particular, where a long-term treatment with aninjection is required, the desired pharmacological effects can beachieved in a stable manner by injection of the preparation once a week,once a month, or even once a year, instead of daily administration.Thus, said preparation can achieve a sustained drug release over alonger period as compared with the prior art sustained-releasepreparations.

(2) When the preparation in which a biodegradable polymer is used isadministered in the form of an injection, such surgical operation asimplantation is no more required but the preparation can be administeredsubcutaneously or intramuscularly with ease in quite the same manner asthe ordinary suspension injections. There is no need for taking it outagain from the body, because the biodegradable polymer is used.

The preparation can also be administered directly to tumors, the site ofinflammation or the site where there is a receptor, for instance,whereby systemic side effects can be reduced and the drug can be allowedto act on a target organ efficiently for a long period of time.Potentiation of the drug activity is thus expected. Furthermore, thepreparation can be administered intraarterially in the vasoembolictherapy for kidney cancer, lung cancer and so forth as proposed by Katoet al. [Lancet, volume II, pages 479-480 (1979)].

(3) The release of the active ingredient is continuous, so that, in caseof, for instance, hormone antagonists or receptor antagonists strongerpharmacological effects are obtained as compared with daily or frequentadministration.

(4) As compared with the conventional method of production ofmicrocapsules which comprises preparing a W/O/W triple-phase emulsionand subjecting the emulsion to an in-water drying method, the methodaccording to this invention makes it possible to allow the water-solubledrug, which is the active ingredient, to be taken up into microcapsulesefficiently. In addition, there can be obtained fine microcapsuleshaving a good degree of sphericity.

In accordance with the method of this invention, the rate ofwater-soluble drug take-up into microcapsules can be increased markedlyby adjusting the viscosity of the W/O emulsion to a value higher thanthat employed in the conventional processes. Accordingly,sustained-release microcapsules containing a water-soluble drug can beproduced with advantage.

The following examples illustrate the invention in further detail. Inthe following Examples, the weight-average molecular weight is based onstandard of polystyrene.

EXAMPLE 1

Interferon α (500 mg) was dissolved in 300 mg of water at 50° C. Thesolution was added to a solution of 3,500 mg of polylactic acid(weight-average molecular weight: 21,000) in 4 ml of methylene chlorideand the mixture was stirred in a small-size homogenizer(Polytron,product of Kinematica, Switzerland) for 20 seconds. The thus-obtainedW/O emulsionwas cooled to 15° C. in a hermetically closed vessel anddefoaming and liquid temperature adjustment were conducted. The emulsioncooled to 15° C. had a viscosity of 4,500 cp as measured with anUbbelohde viscometer. This emulsion was then dispersed in 500 ml of a 5%aqueous solution of polyvinyl alcohol (PVA) using a homogenizer to givea (W/O)/W emulsion. On that occasion, the homogenizer was operated at4,000 rpm for 1 minute. Thereafter, the (W/O)/W emulsion was stirredgently with an ordinary stirrer for 2 hours to thereby allow theevaporation of methylenechloride, hence the solidification ofmicrocapsules, to proceed. The microcapsules were then collected bycentrifugation and rinsed with purified water on the same occasion. Themicrocapsules collected were lyophilized to obtain a powder.

The content of interferon α taken up in the microcapsules was 11.5%, therecovery rate (take-up rate) being 92.0%.

EXAMPLE 2

Leuprolide (450 mg) and 50 mg of sodium carboxymethylcellulose (Na-CMC)were dissolved in 500 mg of water at 60° C. The solution was added to asolution of 4,000 mg of lactic acid-glycolic acid copolymer (lacticacid/glycolic acid=75 mole %/25 mole %, weight-average molecular weight:12,000) in 4.5 ml of methylene chloride and the mixture was stirred in aPolytron homogenizer for 20 seconds. The thus-obtained W/O emulsion hada viscosity of 3,300 cp at 15° C. The subsequent steps were operated inthe manner of Example 1 to give microcapsules. The content of leuprolidein the microcapsules was 9.8%, the recovery (take-up) being 98%.

EXAMPLE 3

Cefotiam dihydrochloride (50 mg) and 20 mg of gelatin were dissolved in250mg of water at 40° C. The solution was mixed with a solution of 4 gof polylactic acid (weight-average molecular weight: 30,000) in 6.3 mlof chloroform and the mixture was stirred to give a W/O emulsion. ThisW/O emulsion was placed in a glass syringe and adjusted to 16° C.Then,the emulsion was injected into 1,000 ml of a water phase containing0.1% (weight/weight) of Tween 80 and having a temperature of 16° C.while stirring at 7,000 rpm for 1 minute for emulsification. Thechloroform was then allowed to evaporate while stirring at 2,000 rpm for3hours, followed by filtration, which gave microcapsules of 5 to 80 μminsize. In this example, the W/O emulsion had a viscosity of about 180cp. The take-up of cefotiam into the microcapsules amounted to 85%.

EXAMPLE 4

Leuprolide (450 mg) and 90 mg of gelatin were dissolved in 1 ml ofdistilled water to give an aqueous phase. A solution of 4 g of lacticacid-glycolic acid copolymer (lactic acid/glycolic acid =75 mole %/25mole%, weight-average molecular weight: 14,000) in a mixture of 6 ml ofmethylene chloride and 1.5 ml of n-pentane was used as the oil phase.The aqueous phase was gradually added to the oil phase while stirring atroom temperature with a turbine-shaped mixer. The thus-produced W/Oemulsion showed a viscosity of 70 cp at 24° C.

A 0.5% aqueous solution of polyvinyl alcohol (500 ml) was cooled to 15°C. Into this solution, there was injected gradually the above W/Oemulsion while stirring with a homogenizer. The thus-produced (W/O)/Wemulsion was stirred gently with a propeller-shaped stirrer at roomtemperature for about 4 hours to thereby cause evaporation of methylenechloride and n-pentane and solidification of the oil phase. The oilphase in solid form was collected by centrifugation. Theleuprolide-containing microcapsules thus obtained were rinsed with waterand lyophilized into a powder. The take up of leuprolide into themicrocapsules amounted to 89%.

EXAMPLE 5

Leuprolide (495 mg) and 80 mg of gelatin were dissolved in 0.5 ml ofdistilled water to give an aqueous phase. A solution of 3,970 mg oflacticacid-glycolic acid copolymer (lactic acid/glycolic acid =75 mol%/25 mole %, weight-average molecular weight: 14,000) in 5.5 ml ofmethylene chloride was used as the oil phase. The aqueous phase wasgradually added to the oil phase while stirring at room temperature witha turbine-shaped mixer and the emulsion was cooled to 18° C. Thethus-produced W/O emulsion showed a viscosity of 310 cp.

A 0.1% aqueous solution of polyvinyl alcohol (1,000 ml) was cooled to18° C. Into this solution, there was injected gradually the above W/Oemulsion while stirring with a homogenizer. The thus-produced (W/O)/Wemulsion was stirred gently with a propeller-shaped stirrer at roomtemperature for about 3 hours to thereby cause evaporation of methylenechloride and solidification of the oil phase. The oil phase in solidform was collected by centrifugation. The leuprolide-containingmicrocapsules thus obtained were rinsed with water and lyophilized intoa powder. The take up of leuprolide into the microcapsules amounted to94%.

What we claim is:
 1. A sustained-release microcapsule for injectioncontaining a water-soluble drug, which is produced by a processconsisting essentially of preparing a W/O emulsion composed of awater-soluble drug-containing solution as the inner aqueous phase and abiodegradable polymer-containing solution as the oil phase, adjustingthe viscosity of the W/O emulsion used in preparing the W/O/W emulsionto from about 150 to about 10,000 centipoises by the procedures ofincreasing the polymer concentration in the oil phase; adjusting theratio of the aqueous phase to the oil phase; adjusting the temperatureof said W/O emulsion; adjusting the temperature of the external aqueousphase; adjusting the temperature of the W/O emulsion with a line heateror cooler or the like in infusing the W/O emulsion into the externalaqueous phase; or carrying out the above procedures in combination,dispersing said emulsion in an aqueous phase and subjecting theresulting W/O/W emulsion to an in-water drying to form microcapsules. 2.A microcapsule as claimed in claim 1, wherein the viscosity of the W/Oemulsion in preparing the W/O/W emulsion is adjusted to about 150 to5,000 centipoises.
 3. A microcapsule as claimed in claim 1, wherein theviscosity of the W/O emulsion in preparing the W/O/W emulsion isadjusted to about 150 to about 10,000 centipoises by the manner ofregulating the temperatures of (i) the W/O emulsion or (ii) both the W/Oemulsion and the external aqueous phase to from about -20° C. to theboiling point of the organic solvent used.
 4. A microcapsule as claimedin claim 3, wherein the temperature is about 0° C. to 30° C.
 5. Amicrocapsule as claimed in claim 1, wherein the polymer concentration inthe oil phase is increased to about 10 to 80%
 6. A microcapsule asclaimed in claim 1, wherein the ratio of the aqueous phase to the oilphase is adjusted to the range of about 1% to 50%.
 7. A microcapsule asclaimed in claim 1, wherein the water-soluble drug is a biologicallyactive polypeptide.
 8. A microcapsule as claimed in claim 7, wherein thebiologically active polypeptide is(Pyr)Glu-His-Trp-Ser-Tyr-D-Leu-Leu-Arg-Pro-NH-C₂ H₅.acetate.
 9. Amicrocapsule as claimed in claim 1, wherein the polymer is polylacticacid.
 10. A microcapsule as claimed in claim 1, wherein the polymer is acopolymer of lactic acid and glycolic acid.
 11. A microcapsule asclaimed in claim 10, wherein the ratio of lactic acid: glycolic acid ofthe copolymer is about 75±2 mole %: about 25±2 mole %.
 12. Amicrocapsule as claimed in claim 1, wherein the in-water drying isconducted by allowing the W/O/W emulsion to stand under stirring.
 13. Amicrocapsule as claimed in claim 1, wherein the in-water drying isconducted by gradually reducing the pressure while stirring with apropeller-shaped stirrer, magnetic stirrer or rotary evaporator.